Reconfigurable phononic crystal sensor for liquid detection

We propose a reconfigurable phononic crystal (PnC) for detecting the concentration of solutes in liquids. The designed PnC consists of liquid-filled hollow pillars and connecting bars. The finite element method is used to calculate the transmission spectra and band structures of PnC filled with various liquids. We fabricate 3D printed samples and conduct corresponding experiments. The results show that sound velocity is the key parameter affecting the frequency of the passing band. As the sound velocity increases, the resonance frequency shifts down. For both NaCl solution and ethanol solution, good linear relationships between the resonance frequency and liquid concentration are established. Experimental results show good agreement with simulations, and stable detection capabilities are maintained in the presence of interference. The impact of fabrication tolerances on sensor performance has also been discussed, with a greater impact on sensitivity and a smaller impact on Q-factor. The reconfigurability also shows the potential of the design of multi-liquid PnC sensors.